The present invention relates to a mobile communication system, management agent apparatus, and server function moving method and, more particularly, to a method of connecting a mobile node to a network after the mobile node moves in the mobile communication system.
For Mobile IP (Internet Protocol) in a conventional mobile communication system of this type, when a mobile node (MN) moves and is connected to a foreign network, as shown in FIG. 14, it acquires the care-of address CoA (Care of Address) of the foreign network, and requests a home agent (HA) to register the position of the mobile node (e1 and e2 in FIG. 14). The home agent registers the home address HoA (Home of Address) and CoA of the mobile node (e3 and e4 in FIG. 14) (see, e.g., reference 1 (Japanese Patent Laid-Open No. 2002-094557)).
For SIP (Session Initiation Protocol), the mobile node moves, acquires an address in a foreign network, and transmits a registration request via an SIP server (proxy), as shown in FIG. 15 (f3 and f4 in FIG. 15). Then, the mobile node registers the destination address in the SIP server having a registration function (f5 and f6 in FIG. 15). Assume that a server serving as a communication partner of the mobile node is separately registered in the SIP server (f1 and f2 in FIG. 15).
When the mobile node and server are managed by separate SIP servers, the server serving as a communication partner of the mobile node is registered in the SIP server of the server, as shown in FIG. 16 (g1 and g2 in FIG. 16). The mobile node moves, acquires an address in a foreign network, and transmits a registration request via the SIP server (proxy) (g3 and g4 in FIG. 16). Then, the mobile node registers the destination address in the SIP server having the registration function for the mobile node (g5 and g6 in FIG. 16).
By this processing operation, when moving to a foreign network, the mobile node acquires an address in the foreign network, registers the address in the home agent or SIP server having the registration function, and thereby establishes a session with the server.
In the conventional mobile communication system described above, a mobile node 3 cannot select any server optimal for a destination, as shown in FIG. 17. The transmission delay to a server 1 is large, the throughput is low, the response time is long, and it is difficult to provide information corresponding to the destination.
To solve these problems, some conventional mobile communication systems employ broadcast and anycast as means for selecting a server corresponding to a destination. However, the broadcast method requires a dedicated server in a foreign network. The anycast method cannot establish any TCP (Transmission Control Protocol) session, and it is hard for an application to cope with the method.
In a conventional mobile communication system, load balancing using DNSs (Domain Name Systems) 51 to 53, as shown in FIG. 18, is proposed as a method of dynamically selecting a server. According to this method, however, inquiries to the DNS 53 having servers 1-1 to 1-3 are made at many stages, the position of the mobile node 3 is concealed, and no optimal server can be selected. An optimal server can be selected in only the same domain managed by the DNS 51 which can directly communicate with the mobile node 3.
As described above, regardless of the DNS method or the method using a load balancer which typifies a general-purpose server, the conventional load distribution method can distribute the load by only a predetermined server function. Another server function cannot be provided to another user.